The controlled design and synthesis of metal-organic coordination polymers from the self-assembly of simple molecular building blocks is of intense interest due to the promise of generating functional materials.1,2 Vapochromic materials, which display optical absorption or luminescence changes upon exposure to vapors of analytes, such as volatile organic compounds (VOCs), have been a focus of attention due to their potential applications as chemical sensors.9-15 For example, when exposed to certain organic solvents, the extended Prussian Blue Co2+—[Re6Q8(CN)6]4− (Q=S, Se) system yields dramatic changes in the visible spectrum that are attributable to the sensed solvent impacting the geometry and hydration around the CoII centers.15 
Several vapochromic compounds based on AuI, PdII, and PtII coordination polymers have also been reported.9-14 The vapochromism in these systems is based on changes in both the visible absorption and emission spectra. In the linear {Tl[Au(C6Cl5)2]}n polymer, weak interactions between the Tl atoms and the adsorbed VOC molecules modify slightly the color, and more significantly the emission spectra.12 On the other hand, changes in the emission spectra of [Pt(CN—R)4][M(CN)4] (R=iso-C3H7 or C6H4—C6H4—CnH2n+1; n=6, 10, 12, 14 and M=Pt, Pd) occur when metal-metal distances are modified due to the presence of VOC molecules in lattice voids; small changes in the absorption spectrum can also be observed.13,16 Another example is the trinuclear AuI complex with carbeniate bridging ligands, for which its luminescence is quenched in the solid-state when C6F6 vapor is adsorbed due to the disruption of Au—Au interactions.11 
Some of these vapochromic materials have recently been incorporated in chemical sensor devices. For example, [Au—(PPh2C(CSSAuC6F5)PPh2Me)2][ClO4] has been used in the development of an optical fiber volatile organic compound sensor.17 A vapochromic light emitting diode18 and a vapochromic photodiode19 have also been built using tetrakis(p-dodecylphenylisocyano) platinum tetranitroplatinate and bis(cyanide)-bis(p-dodecylphenylisocyanide)platinum(II), respectively.
In these previous discoveries, slight shifts in the νCN stretch are observed if hydrogen-bonding between the N(cyano) atoms and the VOC molecules present in the lattice occurs. Importantly, VOCs cannot be readily differentiated or identified via IR spectroscopy in this case since νCN shifts of only 0-10 cm−1 are usually observed.17,54,55 
To overcome the shortcomings of the prior art, the need has arisen for coordination polymers having improved vapochromic properties for enhancing the sensitivity of analyte detection. The IR signatures achieved by the present invention are unusually diagnostic for a particular analyte, both in the number and position of the IR bands. In the case of some gases, the adsorption of the analyte to the polymer substantially enhances the IR response. That is, the response in the νCN or other pertinent region of the spectrum is extremely strong compared to the direct IR-signature of some gases, which is the current state-of-the-art in gas sensors. Moreover, in the present invention the vapochromism of polymers can be readily and reversibly observed by multiple means, such as visible colour changes and luminescence changes in addition to IR spectroscopic changes.